Walking mechanism for excavating machines



June 14, 1966 o. HOFFMANN ETAL 3,255,836

WALKING MECHANISM FOR EXCAVATING MACHINES Filed Dec. 23, 1965 5 Sheets-Sheet 1 HUT/ W F/6.1

r- JZ Otto HoppmQhn QIL J'. Franz-Josef Platt@ .Iun14, 1966 o. HOFFMANN ETAL 3,255,836

WALKING MECHANISM FOR EXCAVATING MACHINES Filed D60. 25, 1965 5 Sheets-Sheet 2 f F/s. 2

inver-:fors:

Otto Happmann Karl J'. Klei n Franz -Crose Platte June 14, 1966 o. HOPPMANN ETAL 3,255,836

WALKING MECHANISM FOR EXCAVATING MACHINES Filed Dec. 25, 1965 5 Sheets-Sheet 5 75 lnvenfors:

Otto Hoppmanh Karl 3'. Klein Franz-Josef Platte June 14, 1966 o. HOFFMANN ETAL 3,255,836

WALKING MECHANISM FOR EXCAVATING MACHINS Filed Dec. 23, 1963 5 Sheets-Sheet 4 lnven0rs= Otc Hoppmann Kar'L T. Klein Franz-fosa? Plattc June 14, 1966 o, HOPPMANN ETAL 3,255,836

WALKING MECHANISM FOR EXCAVATING MACHINES lh 5 Sheets-Sheet 5 v Filed Deo. 2E, 1965 am a ra a .mm m Ph nPmF eolte VHKM /n I.. o/.u

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United States Patent O 3,255,836 'WALKING MECHANISM FOR EXCAVATING MACHINES Otto Hoppmann, Mulheim an der Ruhr, Karl J. Klein,

7 Claims. (C1. iso-s) The present invention relates to an excavating machine with a so-called walking mechanism. It is known to equip surface or open pit mining machines with a so-called walking mechanism instead of full tracks or caterpillars. These walking mechanisms are actuated mechanically or hydraulically and operate in the -foll-owing manner. With each step, the front portion of the machineframe is lifted by means of feet contacting the ground and is simultaneously moved forward, w-hereas the rear portion of the machine frame is usually dragged over the ground. The advance of the machine or device is thus brought about by a continuous lifting, tilting and lowering of the machine frame. Such walking mechanisms are not applicable in all instances, especially not for bucket wheel excavators With which the walking operation is intended to be employed for adjusting the excavating or scraping depth. In this instance, it is required that the machine advance by means of the walking mechanism practically without changing its location as to height so that the scraping operation will not be interfered with. This requirement has been met by other heretofore known walking mechanisms for excavators. These walking mechanisms comprise two pairs of skid-like tracks on which the excavartor understructure is supported alternately by means of circular sector-shaped rollers. While the understructure of the excavator moves on the tracks of one pair of tracks by means of the downwardly directed arched or curved race surface of the rollers, the track skids of the other pair which are lifted off the ground are moved forwardly. Inasmuch as the two track skids arranged on both sides of the -machine are spaced from each other by relatively small distances only, with this design of excavators, the two pairs of track skids which approximately are of the same length can be turned relative to each other by a very small angle only. Consequently, the excavator when advancing can move along rather at curves only.

According to another embodiment of excavators of the general type involved, the track skids of one pair of skids are so short that they can be tilted by 360 between the track skids of the other pair. However, as far as the support of the machine on the track skids is concerned, only a correspondingly small supporting base is available. Moreover, with this arrangement the track skids do not easily adapt themselves to rather irregular ground contours and are not suitable for moving over great inclines.

It is, therefore, an object of the present invention to provide a walking mechanism for excavators and the like which will be able to advance practically without changing their location as to height.

It is another object of this invention to provide an excavator as set forth in the preceding paragraph, which excels by its steadiness.

Still another object of this invention consists in the pro- Vision of an excavator which will be able to move over irregular ground contours with considerable inclines.

It is a still further object of this invention to provide an excavator equipped witha walking mechanism, which will be considerably lighter than heretofore known excavators of the above-menttioned character having the same output.

These and oher objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGURES 1 and 2 respectively illustrate in different positions the lower portion of a bucket excavator seen from the side while moving along a straight line;

FIGURES 3 and 4 respectively represent top views of FIGURES 1 and 2;

FIGURE 5 illustrates a section along the line V-V of FIGURE 3;

FIGURE 5a is a section similar :to that of FIGURE 5 but showing the lower portion of the bucket excavator in a different position;

FIGURE 6 is a top view of the lower portion of the excavator with the excavator understructure turned relative to the legs resting on the ground;

FIGURE 7 is a side View of the lower portion of an excavator according to the invention on an inclined groun'd.

FIGURE 7a is a V-iew showing the mechanism for moving the excavator structure on the platform therebeneath and drawn at a larger scale than FIGURE 7;

FIGURES 8 to 13 illustrate in section and plan view a simplified and modified arrangement according to the present invention in that the modification of FIGURES 8 to 13 is designed for movement in a straight line only.

'The present invention is based on an excavator, surface remover or the like with a walking mechanism which comprises at least two gro-ups of supporting means which are alternately under the load of the excavator structure, of which at least one of said groups is connected to the excavator frame structure by a rolling mechanism. An excavator according to the invention is characterized primarily in that the excavator frame structure is movable on an intermediate support structure in the form of one or a pair of platforms which support structure -is alternately supported by one group 'of legs or, when the excavator frame is supported by another group of legs, is displaceably suspended on the excavator frame. An excavator according to the invention is furthermore characterized in that the legs on which the foot plates are journalled for three-dimensional movement, are adjustable as to height in order to adapt the excavator to the contour of the ground.

Preferably, the support structure comprises two intermediate'support platforms, each being equipped with one group of supporting legs. One of these intermediate supports is provided with a train of rollers for a straight movement of the excavator frame, whereas the other intermediate support is provided with a train of rollers for a turning movement of said excavator frame about anshaped that they will permit the excavator frame to move relative to said intermediate supports in conformity with the purpose for which said trains of rollers are designed.

Referring now to the drawing in detail, the walking mechanism of the excavator according to the present invention has two groups of supporting means which include legs 1, 2, 3; 4, 5, 6. Each of said groups comprises three supporting legs adjustable as to height. Each of said supporting legs is formed by a piston rod the lower end of which is journalled in a ball joint on a foot plate 7. Piston 8 (FIG. 5) of each supporting leg is reciprocable in a vertically arranged cylinder 9 connected to Ian intermediate support or platform structure 10, 1l respectively. These intermediate supports, or platforms, when seen from the top, have the shape of an equilateral triangle with cutoff corners. One of said intermediate supports, viz. platform 11, is with play inserted into the other intermediate support, in this instance, platform 10, which latter is correspondingly designed as a hollow intermediate member. The arrangement is such that the corners of the intermediate support or platform 11 protrude from the intermediate support or platform 10. The cylinders 9 of the six supporting legs are arranged at the corner portions of the two platforms.

Provided on the top side of the intermediate supports 10, 11 and on both sides of each cylinder 9 are two trains of rollers 12, 13. Each of these trains of rollers comprises a series of flanged rollers. The three pairs of trains of rollers 12 arranged on the intermediate support 10 extend along straight lines parallel to each other, whereas the three pairs of trains of rollers 13 arranged on the intermediate support 11 are curved along circles the center point 14 of which is located in the center of the intermediate support 11.

The understructure or frame structure 15 of the excavator rests on the trains of rollers 12, 13 by means of straight and curved rails 16, 17 respectively, arranged at the bottom side of said understructure 15. The cylinders 9 on the supporting legs protrude beyond the respective platform or intermediate support 10, 11 and extend through cutouts 1S, 19 provided in the excavator understructure 15. The cutouts 18 pertaining to the supporting legs 1, 2, 3 extend along straight lines and are parallel to the trains of rollers 12, whereas the curved cutouts 19 pertaining to the supporting legs 4, 5, 6 are coaxial with the contour confined by the trains of rollers 13. The cylinders 9 have a certain freedom of movement in the cutouts 18, 19 which freedom of movement corresponds to the longitudinal movement and turning movement of the excavator understructure during a step in the straight movement and the turning movement of the excavator, respectively. The upper ends of cylinders 9 are each provided with a collar 20 (FIG. 5) adapted to rest on the upper side of the excavator understructure 15 at opposite sides of said cutouts 18, 19. These collars will rest on said top side of the excavator understructure 15 when piston 8 is lifted by pressure fluid acting on the bottom side thereof so that the foot plate 7 is lifted off the ground. In this instance, the respective intermediate support, for instance 10, will be suspended on the excavator understructure. 15 by means of the cylinders 9 of the three respective supporting legs 1, 2, 3. The rollers of the respective roller trains 12 will simultaneously have been lifted off the rails 16 somewhat in the downward direction, but the rails are still aligned with the rollers. The excavator understructure 15 will then, through the intervention of the roller trains 13, be supported by the other supporting legs 4, 5, 6 the foot plates of which rest on the ground. Under these conditions, the collars 20 of the cylinders 9 pertaining to platform 11 are slightly lifted off from the top side of the excavator frame structure 15.

The upper excavator structure 22 rests on the excavator understructure 15 by means of a ball-supported turntable 21.

When the excavator occupies the position of FIGS. 1, 3 and 5, the understructure 15 thereof will, by means of legs 4, and 6 rest on the ground, and, more specifically, through the intervention of the intermediate support 11 supported by said legs. It will be appreciated that the understructure 15 rests on the roller trains 13 of intermediate support 11 by means of rails 17. The foot plates of the supporting legs 1, 2, 3 are lifted off the ground so that the intermediate support pertaining thereto is supported by the understructure through the intervention of the respective cylinders 9. The intermediate support 10 is, relative to the understructure 15, displaced as far as possible toward the right so that the respective cylinder 9 will be located at the right-hand end of the cutouts 18. This displacement may be effected by means of Winches or hydraulic devices, while the collars 20, through the intervention of sliding surfaces, have been displaced on corresponding surfaces at the top side of the excavator understructure 15.

For purposes of advancing the excavator toward the right, legs 1, 2 and 3 are lowered until the foot plates 7 pertaining thereto rest on the ground. The intermediate support 10 pertaining thereto is, by means of the fluid pressure acting from the top on piston 8, lifted slightly so that the rollers of the roller trains 12 will from below engage the bottom surfaces of the corresponding rails 16 of the understructure 15.

Furthermore, the legs 4, 5 and 6 are shortened so that the foot plate 7 pertaining thereto will be in lifted position over the ground, and the intermediate support 11 will be supported by the understructure 15 through the intervention of the respective cylinders 9.

If, now, the excavator understructure 15 is rolled toward the right on the roller trains 12 into FIGS. 2 and 4 position, the cutouts 18 will move until their left ends abut the stationary cylinders 9 of legs 1, 2 and 3. For purposes of illustrating this advancing movement of the excavator, the original position of the excavator understructure 15 as occupied in FIG. 1, is indicated in FIG. 2 by dot-dash lines.

During the above-mentioned movement of the excavator understructure 15 toward the right, said understructure 15 has carried with it the intermediate support 11 because the cylinders 9 supporting the intermediate support 11 are connected through the cutouts 19 with the understructure 15 and because, furthermore, due to the flanges of the rollers pertaining to the trains 13 and arranged on the intermediate support 11, there exists a connection with the rail 17 on the understructure 15.

For further advancing the excavator in straight direction toward the right from the position of FIGS. 2 and 4, the legs 4, 5 and 6 are lowered so that their foot plates rest on the ground. Furthermore, legs 1, 2 and 3 are shortened so that their foot plates will again be in raised position over the ground. The intermediate support 10 is then, together with legs 1, 2 and 3, displaced toward the right to such an extent that the respective cylinders 9 rest against the right-hand ends of the cutouts 18. In this way, the position according to FIGS. l, 3, and 5 has been restored after completion of the first step. Additional steps will be effected by means of the movements described in connection with FIGS. 1 to 5.

If it is desired to turn the excavator on the spot, the understructure 15 is rested on the corresponding lowered legs 4, 5 and 6. The understructure 15 will then roll on the roller trains 13, for instance in clockwise direction, until the cylinders of the supporting legs 4, 5 and 6 rest against the corresponding ends of the cutouts 19, (see the solid-line position of the understructure 15 in FIG. 6). The understructure 15 during its turning movement about axis 14 takes with it the intermediate carrier 10. The legs 1, 2 and 3 pertaining to said intermediate carrier 10 are now lowered t-o such an extent that their foot plates rest on the ground. Furthermore, legs 4, 5 and 6 are lifted, and the intermediate support 11 now supported by the understructure 15 will, together with legs 4, 5 and 6 be turned in clockwise direction about axis 14 until the cylinders pertaining to legs 4, 5 and 6 rest against the other end of the cutouts. By again lowering the legs 4, 5 and 6 and again lifting the legs 1, 2 and 3, the understructure 15 can be turned in clockwise direction in conformity with the freedom of movement determined by the cutouts 19.

It will thus be appreciated that the excavator can be turned on the spot by 360 and, of course, also in an opposite direction, as indicated in FIG. 6 by dot-dash lines.

It is important that the advancing movement of the excavator will be effected practically without change in its position as to height, so that the cut of the bucket wheel will not be interfered with. The movement of the intermediate support, which at this time does not support the excavator frame, may be effected during the operation of the excavator.

During the advancing movement or the turning movement of the excavator, the latter always rests on three legs which provide sufficient steadiness. During the normal operation of the excavator, the latter rests on six legs which provide a correspondingly large supporting base.

A walking mechanism according to the present invention is particularly advantageous for the support and advance of a surface mining machine on a ground with an unusually steep incline. FIG. 7 illustrates, for instance, how the above-mentioned excavator rests on a ground with an incline of 1:6. More specifically, the supporting legs are moved .out to a different extent, and the foot plates 7, due to their universal joint connection with the legs, automatically -adapt themselves to the inclination. In this connection, it is possible to give the intermediate supports 10 and 11 and the excavator understructure 15 with the upper structure 22, a position with an only slight inclination, for instance, 1:20, or to adjust for a horizontal position the intermediate supports 10, 11 with the excavator understructures 15 and 22, in spite of the steep incline of the ground. In this way the driving and braking forces required in connection with a displacing operation of the excavator structure on the respective roller trains, may be kept to a minimum. The bottom sides of the foot plates 7 are preferably provided with strong spikes 30 which enter the ground and with a very steep incline of the ground, prevent the foot plates from slipping. If corresponding spikes were provided in connection with -track vehicles, they would dig up the ground and require -vantage, over heretofore known track-equipped excavators, that the excavator designed according to the present invention may also be safely employed on ground contours with steep inclines. Moreover, an excavator according to the invention is considerably lighter than corresponding excavators on tracks, while the turning of the excavator on the spot will be greatly facilitated.

` FIG. 7 also shows driving means for moving the excavat-or understructure 15 on the intermediate support lfi. To this end, Winches 23 are mounted on the bottom side of the understructure 15. Cables from said Winches lead in opposite directions to reversing rollers or drums 24 at the understructure 15 and from there to reversing rollers 25 which are journalled on both sides of the winch drum 23 on the intermediate support 10. From here the cable leads to the fixed points on the understructure of the excavator. Corresponding driving means are arranged on the intermediate support 11 for the rotary movement according to FIG. 6. If desired, also, other driving means such as hydraulic driving means or rack-and-pinion arrangements, may be employed.

The bottom side of the excavator-frame structure 15 has journa-lled adjacent each of the three cutouts 18 a winch 23- adapted to be driven by a motor 23a in opposite directions. A rope or cable 24a is wound around winch 23 and extends in a direction parallel to the direction of displacement of frame structure 15 and is passed in opposite directions to reversing rollers 24 which are journalled on the bottom side of frame structure 15. From there rope 24a is guided back to reversing rollers 25 journalled on intermediate support or platform 10` and from there to connecting points on the bearing blocks carrying the rollers 24. By means of Winches 23, -therefore, frame structure 15 may be displaced on rollers 12. Corresponding Winches are also provided adjacent the curved cutouts 19 and serve for rotating the frame structure on rollers 13.

While the arrangement according to the invention has been described as having the intermediate supports 10, 1v1 equipped with three supporting legs, it is, of course, also possible to provide more than three supporting legs for each intermediate support. Thus, for inst-ance, both intermediate supports or one of said intermediate supports only, may be equipped with a four-point support. By employ-ing suitable control devices, it is possible to load the supporting legs uniformly.

An example of a four-p-oint support is shown in FIG- URES 8 to 13. According to FIGURES 8 and 11 platform 42 is carried by the four piston rods 40, of one group of'supporting means, which are moved downwardly. In this instance frame structure 15 rests on rollers 43, and the cylinders of the other group of supporting means with their piston rods 41 elevated are suspended from frame structure 15 by means of the upper collars 20. The cylinders of the first group rest against the left-hand ends of slots 44 provided in platform 42, whereas the cylinders of the second group rest against the right-hand ends of slots 45 arranged in understructure 15.

For purposes of moving the apparatus t-owards the right first, piston rods 41 are moved out until they rest on the ground, while the correspond-ing pistons are subjected to a liquid under pressure from the top. Subsequently, piston rods 40` are lifted by subjecting the pistons pertaining thereto to liquid under pressure fro-m the bottom (see FIGURES 9 and 12) and thereafter the frame structure is displaced towards the right on rollers 43 until the cylinders of the first group engage the right hand ends of slots 44 and the cylinders of the second group engage the lefthand ends of slots 45.

It is, of course, to be understood, that the present invention is, by no means, limited to the particular structures shown in the drawings, but also comprises any modiiications within the scope of the appended claims.

What we claim is:

1. In an earth working machine, especially excavator, having a frame structure: a platform structure arranged below said frame structure, means supporting said frame structure on said platform structure and adapted for permitting said structures to move'relative to each other in a substantially horizontal plane, a first group of supporting means, and a second group of supporting means, said groups lbeing operable independently of each other, each of the support-ing means of said first and second groups including a first member engaging both of said structures, each of said first members engaging one of said structures with a limited freedom of Vmovement in the direction in which said structures are movable relative to each other thereby making possible said movement of said structures relative to each other, each of the supporting means of said first and second groups also including a second member operatively lassociated with a respective first member beneath said platform structure and adapted selectively to be lowered away from and to be retracted toward the respective said first member and said platform structure thereby permitting actuation of said groups of supporting means in such a way that the supporting means of said first group are placed into lowered position for supporting said platform structure with regard to the ground while the supporting means of said second group are in retracted position or to move the supporting means of said second group into lowered position for supporting said frame structure with regard to the ground while the supporting means of said first group are in retracted position, and means operatively connected between said frame structure and said platform structure for effecting the said relative movement of said structures.

2. An earth working machine according to claim 1, in whic-h said second member of said groups comprises a downwardly extending leg and a foot plate at the lower end thereof, and universal joint means linking the said foot plate to said leg.

3. In an earth working machine, especially excavator, having a frame structure: a platform structure comprising a first platform and a second platform and being arranged below said frame structure, first means interposed between said first platform and said frame structure adapted for supporting said frame structure on said first platform and also adapted for permitting a straight movement of said frame structure and said first platform relative to each other, second means interposed between said frame structure and said second platform adapted for supporting said frame structure on said second platform and also adapted for permitting said frame structure and said second platform to move relative to each other along a circular path, a first group of supporting means pertaining to said first platform, and a second group of supporting means pertaining to said second platform, said groups being operable independently of each other, each of the supporting means of said first and second groups including a first member engaging both of said frame structure and the pertaining platform, each said first member engaging one of said frame structure and the pertaining platform with a limited freedom of movement in the direction in which said frame structure and the pertaining platform are movable relative to each other thereby making possible said movement of said frame structure and said platforms relative to each other, each of the supporting means of said first and second groups also including a second member operatively associated with a respective first member and adapted selectively to be lowered away from and to be retracted toward the respective first member and said pertaining platform thereby permitting actuation of said groups of supporting means in such a way that the supporting means of said first group are placed into lowered position for supporting said first platform with regard to the ground while the supporting means of said second group are in retracted position or to move th-e supporting means of said second group into lowered position for supporting said second platform with regard to the ground, each said first member having limited freedom of axial movement relative to said frame structure and the pertaining platform whereby, while the supporting means of each said group are in retracted position the respective said platform pertaining thereto is suspended on said frame structure, and means operatively connected between said platform structure and said frame structure for effecting the said relative movement between said frame structure and the said platforms of said platform structure.

4. In an earth working machine, especially excavator, having a frame structure provided with a plurality of straight parallel slots and also comprising a plurality of curved slots following the contour of a circle, a platform structure comprising a first platform and a second platform and being arranged below said frame structure, first means interposed between said first platform4 and said frame structure adapted for permitting said frame structure on said first platform and also adapted for permitting a straight movement of said frame structure and said first platform relative to each other in the direction of said straight slots, second means interposed between said frame structure and said second platform adapted for supporting said frame structure on said second platform and also adapted for permitting said frame structure and said second platform to move relative to each other along a circular path corresponding to the curvature of said curved slots, a first group of supporting means corresponding in number to the number of said straight slots and a second group of supporting means corresponding in number to the number of said curved slots, said groups being operable independently of each other, each of said supporting means of said first group comprising a cylinder extending substantially perpendicularly to said first platform and having its lower portion connected to said first platform and having its upper portion engaging one of said straight slots for movement therealong, each said cylinder permitting limited movement of said frame structure and the pertaining platform toward and away from each other, each of the supporting means of said second group comprising -a cylinder substantially perpendicular to said second platform and having its lower portion connected thereto and having its upper portion extending into one of the curved slots, each of said supporting means of said tirst and second groups also comprising a piston with a downwardly extending piston rod reciprocable in the respective cylinder of the respective group, each of said supporting means of said first and second groups also including foot plate means universally joined to the lower end of the respective piston rods whereby the foot plate means of said first group may selectively be lowered to the ground and the foot plate means of the second group may be lifted off the ground and Vice versa, and means operatively connected between said platform structure and said frame structure for effecting the said relative movement between said frame structure and the said platforms of said platform structure.

5. An earth working machine according to claim 4, in which the cylinder and pistons of said first and second groups are operable selectively so that either one of said platforms is suspended on said frame structure by the cylinders pertaining thereto when the foot plate means pertaining to the respective other platform rest on the ground.

6. An earth working machine according to claim 4, in which the cylinder portions extending into the slots of said frame structure extend through said slots and are provided with fiange means on the upper side of the frame structure for abutting engagement with the top of said frame structure. y

7. An earth working machine according to claim 4, in which one of said platforms has a portion slidably arranged in a hollow portion of the other platform, and in which said groups of supporting means of said first and second groups are arranged outside said hollow portion of said other platform.

References Cited by the Examiner UNITED STATES PATENTS 1,568,109 1/1926` Ventzlaff 180-8 2,660,253 1l/1953 Davidson 180-8 LEO FRIAGLIA, Primary Examiner. 

1. IN AN EARTH WORKING MACHINE, ESPECIALLY EXCAVATOR, HAVING A FRAME STRUCTURE: A PLATFORM STRUCTURE ARRANGED BELOW SAID FRAME STRUCTURE, MEANS SUPPORTING SAID FRAME STRUCTURE ON SAID PLATFORM STRUCTURE AND ADAPTED FOR PERMITTING SAID STRUCTURES TO MOVE RELATIVE TO EACH OTHER IN A SUBSTANTIALLY HORIZONTAL PLANE, A FIRST GROUP OF SUPPORTING MEANS, AND A SECOND GROUP OF SUPPORTING MEANS, SAID GROUPS BEING OPERABLE INDEPENDENTLY OF EACH OTHER, EACH OF THE SUPPORTING MEANS OF SAID FIRST AND SECOND GROUPS INCLUDING A FIRST MEMBER ENGAGING BOTH OF SAID STRUCTURES, EACH OF SAID FIRST MEMBERS ENGAGING ONE OF SAID STRUCTURES WITH A LIMITED FREEDOM OF MOVEMENT IN THE DIRECTION IN WHICH SAID STRUCTURS ARE MOVABLE RELATIVE TO EACH OTHER THEREBY MAKING POSSIBLE SAID MOVEMENT OF SAID STRUCTURES RELATIVE TO EACH OTHER, EACH OF THE SUPPORTING MEANS OF SAID FIRST AND SECOND GROUPS ALSO INCLUDING A SECOND MEMBER OPERATIVELY ASSOCIATED WITH A RESPECTIVE FIRST MEMBER BENEATH SAID PLATFORM STRUCTURE AND ADAPTED SELECTIVELY TO BE LOWERED AWAY FROM AND TO BE RETRACTED TOWARD THE RESPECTIVE SAID FIRST MEMBER AND SAID PLATFORM STRUCTURE THEREBY PERMITTING ACTUATION OF SAID GROUPS OF SUPPORTING MEANS IN SUCH A WAY THAT THE SUPPORTING MEANS OF SAID FIRST GROUP ARE PLACED INTO LOWERED POSITION FOR SUPPORTING SAID PLATFORM STRUCTURE WITH REGARD TO THE GROUND WHILE THE SUPPORTING MEANS OF SAID SECOND GROUP ARE IN RETRACTED POSITION OR TO MOVE THE SUPPORTING MEANS OF SAID SECOND GROUP INTO LOWERED POSITION FOR SUPPORTING SAID FRAME STRUCTURE WITH REGARD TO THE GROUND WHILE THE SUPPORTING MEANS OF SAID FIRST GROUP ARE IN RETRACTED POSITION, AND MEANS OPERATIVELY CONNECTED BETWEEN SAID FRAME STRUCTURE AND SAID PLATFORM STRUCTURE FOR EFFECTING THE SAID RELATIVE MOVEMENT OF SAID STRUCTURES. 